EP 0 994 003 B1 discloses such a valve apparatus for a pressure-actuated motor vehicle brake system. The known valve apparatus has a pressure medium input to which a pressure source can be connected. A consumer, for example a brake cylinder acting on the wheels of the vehicle, is connected to the pressure medium output. The pressure medium input is controlled by a relay valve which can be actuated via a control input of the valve apparatus. The relay valve comprises a relay piston which, on pneumatic actuation via the control input, repels a valve ring against the return force of a valve spring, whereby the pressure medium input is opened. A pressure-actuatable inlet valve is arranged between the relay valve and the pressure medium output, i.e. the consumer connected to the pressure medium output. The known valve apparatus furthermore comprises a pressure-actuatable outlet valve which controls a fluidic connection of the pressure medium output to a purge of the valve apparatus leading to atmosphere, i.e. connected to the environment of the valve apparatus. This outlet valve is formed as a diaphragm valve and has as a closing member a valve diaphragm which lies on a valve seat and opens against the pressure in a purge chamber of the outlet valve, and in the known valve apparatus against the return force of a valve spring. When the outlet valve is opened, the pressure medium output, and hence the space lying between the inlet valve and the consumer, is purged to atmosphere. For purging, the known valve apparatus has a pressure medium outlet which leads to atmosphere via a damper. The pressure medium output is thus also connected fluidicly to the relay valve.
The pressure-actuatable outlet valve of the known valve apparatus is assigned an electrically actuatable purge valve which guarantees pre-control of the diaphragm valve. The electrically actuatable purge valve serves to control the purging of the outlet valve. Purging of the purge chamber creates pressure conditions at the valve diaphragm of the outlet valve which guarantee the desired opening of the outlet valve for the purpose of purging the consumer. In the known valve apparatus, a purge line controlled by the electrically actuatable purge valve opens into a pressure medium chamber upstream of the inlet valve in the flow direction, so that purging takes place via the relay valve.
For operation of a pressure-actuated brake system, in particular as part of an anti-lock brake system, purging of the outlet valve desirably takes place as quickly and completely as possible, so that the full opening cross section of the outlet valve is available for purging the consumer. It has been found that, in operation of the known valve apparatus, purging of the outlet valve often does not take place quickly enough to meet the requirements. Measurement of the purge times has revealed that the purge time of the brake cylinder, even after normal braking processes, is too long.